This invention relates to rotary valves, and more particularly to butterfly valves with annular seats especially for use under a wide range of temperatures and pressures. Prior art on valves of this type can be found in Class 251 of the classification system of U.S. patents.
Butterfly and other types of rotary valves with annular yieldable seats constructed of Teflon, Kel-F, and other polymeric materials, are well-known and commonly used for controlling the flow of various fluids in a wide variety of industries. Although some of these valves are satisfactory when employed at ambient or moderate temperatures and modest pressures, experience has shown that seats of this type employed in butterfly valves often leak when exposed to extreme temperatures, either elevated or cryogenic, for these seats, like most all other solid material, expand when heated and contract when cooled. This volume change affects all of the dimensions of the seat, and since the extent of expansion or contraction is also dependent upon the material from which the seat is constructed, it is quite difficult to provide a butterfly valve seat that will maintain a fluid-tight seal over a wide range of temperatures when subjected to significantly elevated pressures.
Although seats of yieldable polymeric material are considered to be the most suitable for use in butterfly valves that may be subjected to wide ranges of temperature, when the valve is exposed to extreme cold, as encountered in cryogenic applications, there is a tendency for the seat to shrink away from the metallic valve elements between which it is secured, thereby establishing a leakage path. Another complication is presented if the butterfly valve's disc is opened while the valve is being cooled down, for in this situation the seat tends to contract and warp out of its circular form. Maintaining the opened valve at cryogenic temperatures causes the seat element to stiffen in its warped form, thereby making it very difficult, if not impossible, for the seat to return to its circular shape when the valve is closed, and thus the leakage problem is compounded.
Another problem arises when yieldable polymeric valve seats are subjected to elevated temperatures considerably above ambient. Under such conditions there is a tendency for all the vavle elements to expand, thereby causing excessive interference between the seat and the valve disc, and thus detrimentally affecting the operation of the valve. Furthermore, experience has shown that application of a constant pressure load on the valve at elevated temperatures causes the polymeric seat to exhibit a gradual tendency to flow or creep, even at stresses below the seat's proportional limit.
Earlier attempts to overcome these problems include the use of mechanical springs, fulcrum systems, etc., with or without temperature responsive members, to press the seat against the valve disc and thereby hopefully to eliminate leakage. However successful these prior art solutions might be, the fact remains that the use of springs at extreme temperatures is undesirable because they tend to lose some of their important physical characteristics. For example, when metal springs are exposed to cryogenic temperatures they become stiff and brittle; they could break and thereby permanently disable the valve. When some metal springs are exposed to greatly elevated temperatures they frequently become plastic and lose their ability to exert sufficient pressure on the valve seat to maintain seal integrity. In some cases the prior seat energizing devices take a permanent set and thus fail to exert the required force on the seat when the temperature is lowered, thereby allowing the valve to leak. Furthermore, many of the seat energizing devices heretofore known are unduly complicated, and relatively expensive to manufacture.
Accordingly, one object of the present invention is to provide an improved pressure sensitive, temperature responsive rotary valve.
Another object of the present invention is to provide an improved rotary valve seat having sealing surfaces that are dynamically enlarged in response to an increase in fluid pressure and/or a change in temperature, thereby improving the coaction of the seat with the sealing surface of the valve's flow control element.
Another object of the present invention is to provide a new type of energizer for a yieldable seat in a rotary valve, the energizer providing uninterrupted constant pressure on the seat throughout a wide range of temperatures.
Another object of the present invention is to provide an improved rotary valve seat energizer that pressurizes the seat in both radial and axial directions to maintain the seat element in fluid-tight contact with the valve's flow control element at all operating conditions.
Another object of the present invention is to provide an improved butterfly valve with a yieldable seat and a rigid seat energizer that cooperate to provide a constant fluid pressure barrier with the valve's flow control disc without necessitating a significant increase in torque to open or close the valve when high pressures and/or high or low temperatures are encountered.
Another object of the invention is to provide an improved means for preventing diametric movement of a yieldable polymeric valve seat when the seat is exposed to cryogenic temperatures, thus avoiding excessive build up of frictional break-away forces caused by shrinkage of the seat against the valve's flow control element.
Yet another object of the present invention is to provide a new type of energizer ring for a yieldable rotary valve seat, the ring preventing undue distortion of the sealing surfaces of the seat while the valve is subjected to low temperatures when in the open position.
Another object of the present invention is to provide a new means for mechanically loading a yieldable annular seat for a rotary valve, the loading means preventing the escape of fluid to the downstream side of the valve when the valve is exposed to high temperature fluids.
Still another object of the present invention is to provide an improved means for confining a yieldable seat in a rotary valve so that creep of the seat is prevented when the valve is exposed to fluid at high temperature and high pressure.
Additional objects of the present invention will become apparent from the following description of the invention.